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SCIENCE 



[N. S. Vol. XXXI. No. 803 



whicli would not otherwise have been vapor- 

 ized. Furthermore, it is quite possible that 

 the comet, in moving around the sun, en- 

 tangles itself in the stream of material driven 

 from the sun and varies in its effects in ac- 

 cordance with its being or not being in a 

 solar streamer more or less dense for the 

 time being, speaking relatively. It is easily 

 conceivable that an assumed stratification 

 of space may be a cause of variations of 

 comet's tail brightness. Putting it more 

 properly, it is conceivable that a comet may 

 act as an indicator of the condition of space 

 around the sun, the space in which the comet, 

 for the time being, is moving. Even under 

 the idea that there is volatile matter emitted 

 from the sun which ordinarily would not be 

 visible, let such matter strike into the 

 nucleus of a comet and meet matter from the 

 comet itself; it is easily seen that interac- 

 tions, electrical or otherwise, or even physical 

 collisions, may add to the light of a comet's 

 tail. 



The chief point, however, which I have en- 

 deavored to emphasize by the comparisons 

 above made, is the excessive tenuity of the 

 matter which would be sufficient to give rise 

 to a brilliant appendage to a comet and the 

 exceedingly small amount of volatile matter 

 needed. This fact renders it possible that the 

 comet may, in the lapse of many years, re- 

 plenish itseK in the depths of space and may 

 account for the fact that at each return, even 

 to close proximity to the sun, a tail is de- 

 veloped. Otherwise, since the matter of the 

 tail certainly does not return to the comet, it 

 would seem that the volatile matter would be 

 distilled off and lost in a very few perihelion 



Elihu Thomson 



ROBERT PARR WHITFIELD 

 Peofessor Egbert Parr Whitfield died on 

 April 6 at Troy, N. Y., in his eighty-second 

 year. 



Professor Whitfield's association with the 

 progress of paleontological science in the 

 United States has placed his name perma- 

 nently among the pioneers of that science in 



this country. His work, however, has no anti- 

 quarian interest merely. From the first 

 it was forcible, careful and convincing. 

 Throughout the long period of his connection 

 with the American Museum of Natural His- 

 tory he industriously contributed papers on 

 invertebrate paleontology, to the publications 

 of that institution, while his work on the sur- 

 veys of Ohio, Wisconsin and New Jersey was 

 persistently prosecuted, in reports of great 

 value, distinguished always by keen morpho- 

 logical discrimination. 



His work began with his employment on 

 the New York State Survey, where he as- 

 sisted Professor James Hall, who was then 

 engaged in his studies of Paleozoic fossils. 

 Professor Whitfield's assistance was at first 

 in the nature of exact preparatory analyses 

 of the copious material offered for examina- 

 tion, classification and description. About 

 this time he produced the beautiful illustra- 

 tions of graptolites which gave distinction 

 and an unusual interest to the decades of the 

 Canadian Survey, and his painfully minute 

 study upon which superinduced a, fortu- 

 nately, only momentary, danger to his eye- 

 sight. He continued his labors on the survey 

 until 187Y, and helped materially to give pre- 

 cision and a broad zoological basis of com- 

 parison to the reconstructions of the inverte- 

 brate life of the past, in the papers and 

 volumes, written by Professor Hall, not only 

 upon the paleontology of New York, but of 

 western states as well. His studies of the in- 

 ternal loops of various genera of brachio- 

 poda, his delineation of the muscular scars of 

 lingula and his rearrangement of the crinoidal 

 scheme of plates were all very helpful. Suc- 

 ceeding this came his admirable descriptive 

 papers published in the geological reports of 

 Wisconsin and Ohio. Then followed an ex- 

 haustive examination of the upper Devonian 

 lamellibranchs, the results of which were 

 embodied in the subsequent New York sur- 

 vey volumes on these shells. 



When the great Hall collection of fossils 

 came into the possession of the American 

 Museum, Professor Whitfield was invited to 

 take charge of this extraordinary cabinet, to 



